In modern society, elevators have become ubiquitous machines for transporting people and cargo through buildings of multiple stories. As elevators are operated continually throughout the day making frequent stops at various floor levels, the braking system of an elevator plays an important role in the smooth operation of the elevator.
Traction machines such as those used in elevator systems to raise and lower the elevator car utilizing belt-driven or rope driven systems typically employ a mechanical or electromechanical braking system to stop or temporarily hold a particular motion. Electromechanical brakes of elevators, for instance, generally employ a clutch-type braking mechanism for supplying a holding or braking torque that is sufficient for slowing or holding an elevator car at a fixed position. The braking torque supplied by clutch-type brakes may be mechanically produced by the friction that is generated between a rotating brake disk that is rigidly attached to a machine shaft and a set of friction pads that is releasably placed in contact with a surface of the brake disk. The engagement or disengagement of the friction pads is electromechanically controlled by a brake coil. When the brake coil is activated, a magnetic attraction between the armature plates and an electromagnetic core causes the friction pads to disengage from the surface of the brake disk. When the brake coil is deactivated, springs that engage the armature plates urge the armature plates into engagement with the surface of the brake disk. Although such clutch-type brakes have been proven to be effective and are still widely used today in various traction applications such as elevators, and the like, they still have room for improvement.
For instance, a clutch-type brake cannot selectively apply different amounts of force to stop the elevator depending on the type of stop required (e.g. an emergency stop vs. a normal stop). A typical clutch-type brake is limited to its rated torque which is further dictated by the mechanical limits of the brake, material composition of its friction pads, and the like. During an emergency, such as loss of power to the building, the braking system must stop the elevator quickly. Such an emergency stop is often abrupt and causes the elevator car to stop with a jerk, which can be an uncomfortable experience for passengers traveling within the elevator car. Since an elevator braking system provides the same braking torque for a normal stop that it provides for an emergency stop, the elevator car and the passengers within it may experience a jerk every time the braking system is engaged to stop the elevator for an emergency stop. Accordingly, it follows that clutch-type brakes do not offer control or variation of the braking force engaged to stop the elevator.
In light of the foregoing, improvements continue to be sought for providing an effective braking system to safely stop an elevator while maximizing the comfort of the stop for the passengers.